South Sister, also known as “Charity”, is the tallest volcano of the trio, standing at 10,363 feet (3,159 m). The eruptive products range from basaltic andesite to rhyolite and rhyodacite. It is a predominantly rhyolitic stratovolcano overlying an older shield structure. Its modern structure is no more than 50,000 years old, and it last erupted about 2,000 years ago. Although its first eruptive events from 50,000 to 30,000 years ago were predominantly rhyolitic, between 38,000 and 32,000 years ago the volcano began to alternate between dacitic/rhyodacitic and rhyolitic eruptions. The volcano built a broad andesitic cone, forming a steep summit cone of andesite about 27,000 years ago. South Sister remained dormant for 15,000 years, after which its composition shifted from dacitic to more rhyolitic lava. Source: Wikipedia
Data Sources: USGS (Elevation), USDA (Imagery)
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